Recently, various electronic devices are being increasingly used, and the increase of portable electronic devices is particularly notable. Since these portable electronic devices are driven by internal batteries, one or a plurality of series-connected batteries are contained in the device. The service life of the battery is short regardless of whether the battery is a primary battery or a secondary battery. Therefore, to continuously use the device for long periods, the battery must be replaced during use.
For example, if a battery replacement warning is generated by, e.g., a lamp on a keyboard while a notebook personal computer is in operation, the user must close the application and temporarily terminate operation by turning off the power supply and, after replacing the battery, must reboot the computer by turning on the power supply. That is, a considerable time is necessary for replacement and reboot.
Also, if the battery is a chemical battery regardless of whether it is a primary battery or a secondary battery, the environmental problems concerning disposal of the used chemical battery and the problems of energy use efficiency have been highlighted with the recent growing interest in environmental problems and problems of energy use efficiency.